1. Field of the Invention
The present invention is broadly concerned with fertilizer compositions and methods wherein the compositions include gypsum together with an amount of a copolymer adjuvant or additive serving to significantly increase the availability of sulfate and Ca in soil, particularly during the early stages after application of the fertilizer compositions. More particularly, the invention is concerned with such fertilizer compositions and methods wherein the dried residue of an aqueous, very low pH copolymer dispersion (e.g., either a true solution or a mixture) coats the gypsum, especially commercial grade agricultural gypsum, and wherein the copolymer includes respective quantities of maleic and itaconic moieties.
2. Description of the Prior Art
Gypsum is a soft mineral compound formed of calcium sulfate (CaSO4), usually found in nature in the dihydrate form (CaSO4.2H2O). It is colorless to white with a silky, pearly, or waxy luster, and commonly has various colored impurities. Gypsum occurs in nature as flattened and often twinned crystals and transparent cleavable masses called selenite. It may also be granular or quite compact. Gypsum has a number of commercial uses, and is well known as a fertilizer and soil conditioner. In the late 18th and early 19th centuries, Nova Scotia gypsum, often referred to as plaister, was a highly sought fertilizer for wheat fields. Gypsum is also used in ameliorating sodic soils. A significant advantage of gypsum is that it is relatively low in cost, while containing substantial quantities of nutrients; e.g., commercial gypsum grades normally contain about 22% Ca and 17% S.
When applied to soils, gypsum supplies crop-available forms of calcium and sulfate ions. However, owing to the very limited solubility of gypsum in water, positive fertilizing results or soil amendments may require a two or three year program of applications. Hence, although gypsum fertilizer use is well-recognized, the slow action of gypsum does not provide immediate help, either in the form of plant nutrition or soil remediation.
There is accordingly a need in the art for enhanced forms of fertilizer gypsums which accelerate the availability of calcium and sulfate ions in the soil, while at the same time not detracting from the desirable properties of the gypsums.